The present invention relates to a roofing module and to a method and apparatus for making such a module.
There are many applications, such as greenhouses or tennis courts, in which it is desirable to utilize sheets of translucent lightweight plastic material for a roof. However, sealing such sheets against leakage has been difficult to accomplish. One sealing method which is both inexpensive and effective is to bend the opposed side margins of the sheet upwardly at 90.degree. with respect to its body. A U-shaped cap is then installed over the upturned margins of adjacent sheets to join them together and prevent leakage through the resulting gap. This technique is shown, for example, in Rylander, U.S. Pat. No. 3,063,201.
A particularly desirable material for roofing modules of this type is the LEXAN sheet which is made by General Electric Company. The LEXAN sheet comprises top and bottom panels which are separated from one another and joined together by means of parallel ribs, thereby creating a series of elongate channels in the sheet. This material has an exceptionally high strength-to-weight ratio in comparison with other translucent or transparent materials and yet still transmits light to a high degree. Due to its channel configuration, however, LEXAN sheets are difficult to bend and therefore are not susceptible to the above-described system for joining panels.
The present invention provides a method and apparatus which will quickly and inexpensively bend the side margins of LEXAN sheets in order to utilize them as roofing modules. The apparatus comprises a frame having multiple sets of coplanar support rollers which support the sheet as it is being processed. A first set of the support rollers is located at spaced-apart locations across the width of the frame at its inlet end, and a second set is located at spaced-apart locations across the width of the frame at its exit end. ln addition, sets of support rollers are located at spaced-apart locations along both sides of the frame below the side margins of the sheet being processed.
The sheet is transported across the frame on the support rollers by means of an endless conveyor belt which is located medially in the frame and which extends from the inlet end of the frame to approximately three-fourths of the way across its length. Top rollers, which are located above the conveyor at spaced intervals, are separated from the conveyor by approximately the thickness of the sheet. Thus the top rollers force the sheet into contact with the conveyor to ensure non-slip transportation.
Associated with each of the support rollers which support the side of the sheet that is being bent are indexing rollers whose axes are oriented normal to the axes of the support rollers in order to engage the edge of the sheet. A portion of the indexing rollers and the associated support rollers are mounted on a first indexing frame, and the remainder of the indexing rollers and their associated support rollers are mounted on a second indexing frame. The first and second indexing frames are movable, independent of one another, relative to the frame on screw rods which are grounded to the frame.
Associated with each of the support rollers that support the margin of the sheet that is not being bent are squaring rollers, which also are oriented perpendicular to the support rollers in order to contact the edge of the sheet. The squaring rollers and their associated support rollers are attached to a squaring frame which is mounted movable relative to the frame on screw rods.
Located beside the first indexing frame are radiant heaters which heat the top and bottom surfaces of the sheet as it is being transported through the apparatus. While either radiant or infrared heaters will work, they must emit enough energy to soften the plastic material of the sheet across its entire width sufficiently to allow the sheet to be bent.
Located downstream from the heaters, between the first and second indexing frames, is a bending section which is used to bend one margin of the sheet upwardly at a 90.degree. angle with respect to the rest of the sheet. The bending section comprises a series of die support rollers which are coplanar with the remaining support rollers and are located inwardly adjacent to the line about which the sheet is to be bent. Located above a portion of the die support rollers are first die rollers, which are coplanar with the die support rollers and separated from them by approximately one sheet thickness. The first die roller which is contacted by the sheet first has a radially outwardly extending bead on its outer periphery which is forced into the soft heated plastic as the sheet is transported between the die support rollers and the first die rollers to create a trough in the sheet along the fold line.
Outwardly of the die support rollers are second die rollers which are rotatable on axes which are not parallel with one another. The second die roller which is located at the beginning end of the bending section has an axis which is parallel with the plane of the sheet, and the second die roller which is located at the finish end of the bending section has an axis which is perpendicular to the sheet. The orientation of the axes of the intermediate second die rollers vary progressively between these two extremes.
In addition to the previously described die rollers, the bending section has third die rollers which are mounted on axes that are perpendicular to the plane of the sheet. The third die rollers are located across from the last and next to the last second die rollers.
In operation, a sheet of material is fed into the inlet end of the apparatus where it is pinched between the conveyor and one of the top rollers. The conveyor then feeds the sheet past the heaters which heat its top and bottom surfaces along the line it is to be folded about. The sheet then is fed into the bending section where the bead on the leading first die roller forms a trough in the plastic which has been softened by the heaters. As the sheet continues through the bending section, the second die rollers cause the margin of the sheet to be bent upwardly along the trough, and the bent margin then is oriented at 90.degree. with respect to the rest of the sheet between the third die rollers and the second die rollers which are located at the end of the bending section.
Once the entire sheet has passed through the apparatus it is turned around and passed through again to bend the other margin.
Accordingly, it is a principal object of the present invention to provide thermoplastic sheets, of the type that have a plurality of rectangular channels passing medially through them, having opposed side margins which are bent upwardly at 90.degree. with respect to the body of the sheet.
It is a further object of the present invention to provide a method for bending the margins of such sheets at a 90.degree. angle.
It is a still further object of the present invention to provide an apparatus for bending the margins of such sheets at a 90.degree. angle.
It is a further object of the present invention to provide such an apparatus in which a margin is bent continuously as the sheet passes through the apparatus.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.